The present invention relates to a hydraulic damper and, particularly, to hydraulic dampers of the type wherein the resisting force can be adjusted from the outside of the dampers.
One of the prior art hydraulic dampers of this type comprises a cylinder containing oil therein, a piston rod one end of which projects out of the cylinder and the other end of which extends into the cylinder, a piston connected to the inner end of the piston rod and dividing the interior of the cylinder into two chambers, a connecting passage connecting the two chambers in the cylinder with each other through a hollow portion formed in the piston rod, a rod member rotatably disposed in the hollow portion of the piston rod, a valve mechanism connected to the inner end of the rod member for changing the opening of the connecting passage, and an adjustor connected to the outer end of the rod member for rotating the same.
The opening of the connecting passage acting as a part of the valve mechanism has usually been formed as one or more orifices formed in the piston rod, so that there is the shortcoming that the range of adjustment is relatively narrow since the effective area of the orifices cannot be increased very much because of the limitation in the diameter of the piston rod and of the hollow configuration.
Moreover, there is a further shortcoming such that it is difficult to know the respective adjusted conditions from the outside and it is necessary to provide a device for indicating the respective adjusted conditions since the rod member of the known hydraulic damper is adapted to rotate through 360 degrees, and it has been difficult to cause the relative angular position of the adjustor and the rod member to coincide in connecting the adjustor and the rod member.